Wind power is considered one of the cleanest, most environmentally friendly energy sources presently available, and wind turbines have gained increased attention in this regard. A modern wind turbine typically includes a tower, a generator, a gearbox, a nacelle, and a rotor having a rotatable hub and one or more rotor blades. Each rotor blade is typically attached to the rotatable hub by a pitch bearing. The rotor blades capture kinetic energy from the wind using known airfoil principles and transmit the kinetic energy through rotational energy to turn a shaft coupling the rotor blades to a gearbox, or if a gearbox is not used, directly to the generator. The generator then converts the mechanical energy to electrical energy that may be deployed to a utility grid.
To ensure that wind power remains a viable energy source, efforts have been made to increase energy outputs by modifying the size and capacity of wind turbines. One such modification has been to increase the length and surface area of the rotor blades. Increasing the rotor blade length, however, may increase loading on other components of the wind turbine. For example, loads experienced by the rotor blades are at a maximum at the pitch bearing. Thus, increasing the length of the rotor blade may require larger and more expensive pitch bearings. Further, transportation costs increase along with increases in rotor blade surface area and length.
As such, efforts have been made to increase energy output of the wind turbine without increasing the length of the rotor blades. For example, hub extensions installed between the hub and the rotor blade have been utilized; however, such extensions do not have an airfoil profile and do not increase energy output. Other wind turbines have utilized a hub airfoil section around the hub extension. Such a fairing may produce some power but does not pitch with the blade; therefore, at off-design wind speeds and directions these fairings produce very little power.
Accordingly, there is a need for a hub assembly for a wind turbine that increases energy output without increasing load on a pitch bearing and without increasing transportation costs. More specifically, a hub assembly for a wind turbine having improved aerodynamic properties would be desired in the art.